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LED Label Metrics Cheat Sheet (DRAFT) by [deleted]

Understanding Label on LED bulbs

This is a draft cheat sheet. It is a work in progress and is not finished yet.


Planning an LED retrofit? Low energy consum­ption and a long life make solid state lighting an attractive option, but deciph­ering the lighting metrics on product packages and spec sheets can be confusing.

The DOE establ­ished the LED Lighting Facts program to ensure one consistent source of inform­ation about all LED products. Lighting Facts labels include five basic metric

These are the most common metrics used by LED vendors will help you understand the ratings.

Color temper­ature (CCT)

Color temper­ature charac­terizes how “cool” (blue) or “warm” (yellow) a white light appears. Ratings are expressed in Kelvins (K). Lower numbers around 2500-3000K indicate warmer light, mid-range values of 3500-4000K are generally considered fairly neutral and white, and higher temper­atures appear cooler.

Color Rendering Index (CRI)

This metric indicates how accurately a light surface renders color as determined by tests with color samples. The ratings typically fall into a 0-100 range, with a standard incand­escent lamp achieving 100, though it’s possible to get a negative score. A source with a CRI in the 70s is acceptable for interior lighting, according to the DOE, but a CRI of 80-90 would be even better.

Two light sources that have the same CCT and CRI may still not render colors the same way, but the two factors still serve as a good starting point for evaluating color perfor­mance – the real test will come when you perform your own visual evalua­tion.

Lumen output

The quantity of light that leaves the lamp. The higher the number, the more light provided.



Lighting Facts labels also provide the input wattage of the lamp. Use it to project energy savings based on the lighting system you’re replacing with LEDs.


Expressed in lumens per watt, the efficacy rating denotes how much light the product puts out for every watt of electr­icity it uses.

Lifetime Metrics

In addition to the basics on energy input, lumen output and color perfor­mance, spec sheets offer a wealth of other inform­ation that can help you make a decision. Consider these metrics to help you narrow down your product choices.

Useful life

Lifetime ratings represent approx­imately how many hours of operation it will take before the LED’s light output has declined to 70% of the initial lumens, referred to as lumen mainte­nance and often abbrev­iated as L70. The DOE recommends asking the fixture manufa­cturer for test data to support the life claims on the package.

Expected lumen mainte­nance

The calculated L70 value sometimes exceeds the intended product use cycle or the lifetime of another lighting system component, the DOE explains. An altern­ative method of calcul­ating lumen mainte­nance perfor­mance involves predicting what the lumen mainte­nance will be at a fixed time interval, such as 25,000 hours.